OCTOBER 1989 - City of Boulder

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2 MAMMALIAN SPECIES 167 FIGURE 2. Dorsal, ventral. and lateral views of skull, and lateral view of lower jaw of Reithrodontomys megalotis megalotis (TlTJ 32227, female) from 6 mi N, 6 mi E Ft. Davis, Jeff Davis Co., Texas. The greatest length of skull is 21.9 mm. Tamaulipas (Goodwin, 1954) frequently have a buffy pectoral spot. as do many individuals of R. m. longicaudw from the San Francisco Bay area (Fisler, 1%5). Albinism is a rare recessive condition similar to that found in Mu (Egoscue, 1958). Selected average and extreme external and cranial measure- ments (mm) from a serits (n = 85) of R. megalotis from Indiana ' (Whitaker and Mumford, 1972), followed by one (n = 15) from western Texas and another (n = 11) from southern Oaxaca, both after Hooper (1952). are, respectively: total length, 126.8 (114 to 146). 133 (120 to 152). 144 (135 to 154); length of tail, 58.3 (50 to 69), 68 (61 to 78). 73 (64 to 83); length of hindfoot, 16.3 (15 to 18). 17 (16 to 18), 17 (15 to 18); length of ear from notch, -, 14 (12 to 15). 14 (13 to 15); greatest length of skull, 20.4 (19.0 to 21.4). 20.5 (19.6 to 21.2), 21.3 (20.0 to 22.5); zygomatic breadth, -, 10.4 (10.0 to 11.0). 10.5 (10.1 to 10.8); breadth of braincase, 10.0 (9.6 to 10.7). 9.9 (9.5 to 10.3). 9.7 (9.0 to 10.1); interorbital breadth, 3.2 (2.7 to 3.8). 3.0 (2.9 to 3.2). 3.0 (2.8 to 3.2); length of palate, 3.6 (3.2 to 4.0). 3.4 (3.2 to 3.7). 3.3 (2.9 to 3.5); length of maxillary toothrow, 3.1 (2.8 to3.5). 3.3 (3.2 to3.5). 3.3 (3.0 to3.4). Fisler (1%5) and Jones and Mursalogu (1%1) Listed mea- surements for large series from California and the Central Great Plains. respectively. The latter authors found secondary sexual variation in mensural characters to be less than individual variation in populations on the Great Plains. DISTRIBUTION. The distribution of the western harvest mouse is mapped in Fig. 3. It is known from southwestern Canada (British Columbia, Alberta, and Saskatchewan) southward to southern Mixico (Oaxaca and Veracmz), and from California eastward to recently-invaded Indiana (Ford. 1977; Whitaker and Mumford. 1972). The species is known altitudinally from 250 feet (about 77 m) below sea level at Death Valley, California. to approximately - FIGURE 3. Distributioo of Reithrodontomys megalotis in Canada and the United States (above) and Mixico (below). Subspecies are: 1, R. m. Jticola; 2, R. m. amoles; 3;R. m. arkonensis; 4, R. m. aztecus; 5, R. m. corrrlirure; 6. R. m. distichlis; 7, R. m. dychei; 3, R. m. hoopen; 9, R. m. limicola; 10, R. m. longicaudus; 11, R. rn. megolotis; 12, R. rn. peninsulae; 13, R. m. ravw; 14, R. m. santacruzae; 15. R. m. saturatus; and 16, R. m. zacatecae. Note that the ranges of saturatus and zacatecae' are thought to overlap in Jalisco. 13,000 feet (4,000 m) on volcanos Popocatipetl and Orizaba in Mixico (Hooper, 1952). FOSSIL RECORD. Reithrodontomys cf. megalotis is known from Sangamon fossil beds in the Cragin Quarry Fauna. Kansas (Hibbard and Taylor, 1960). Illinoian remains from the Mt. Scott Fauna, Kansas, are referable to Reithrodontomys, and have styles and stylids similar to those of megalotis (Hibbard. 1%3). Jakway (1958) assigned late Pleistocene remains from San Josecito Cave, Nuevo Le6n. to R. megaloris. FORM. The glans penis and os penis, figured by Hooper (1959) and Burt (1960). respectively, are morphologically similar to those of Peromyscus. The elongate phallus is rod-shaped and four to five times greater in length (6.0 mm) than in diameter (1.3 mm). The shaft is armored with small proximally-directed spines. but the terminal segment is aspinous. The os penis is a simple bone of uniform thickness that gradually arches upward from a dorsoventrally flattened and laterally expanded base; it lacks a cartilagenous tip. Geographic variation in total length of baculum (6.2 to 9.2 mm) and basal width (0.5 to 1.1 mm) is moderate, with specimens from Mixico averaging slightly larger than those from the United States (Burt, 1960). Males have a welldeveloped vesicular, paired ampullary and Cowper's glands. and four pairs of ventral prostate glands; however, they lack preputial glands (hata. 1964). Average vagina length of seven estrus females was 17.3 mm (Fisler, 1965). The
MAMMALIAN SPECIES 167 hyoid apparatus. albeit slightly smaller. is similar to that of the subgenus Peromyscus (Sprague. 1W1). There are small seba- ceous, and mucous glands associated with the buc- cal cavity (Quay, 1965). Small intestine and rectcrcolon lengths are 3.1 and 1.4 times that of the body length. respectively (Fisler. 1965). FUNCTION. According to Fisler (1965). western harvest mice maintain a normal body temperature (35 to 38°C) when ex- posed to variable laboratory temperatures (17 to 29'C); however. individuals kept at 4.WC for 14.5 h became torpid with a rectal temperature of 26.S°C. Hibernation has been reponed in Nevada (O'Farrell, 1974). and in captive animals torpor has been recorded (Coulombe, 1970) in response to osmotic stress or water deprivation. Pearson (19606) found the minimum oxygen consumption for R. megalotis to be 2.5 cc g-' h-' at an ambient temperature of33OC, with a metabolic increase of 0.27 cc g-' h-' for each 1°C decrease in ambient temperature. Also, oxygen consumption decreased if mice huddled or utilized a nest, but increased approximately 35% in experimental animals from which the fur had been removed. Adult and fetal body compositions (percent dry weight) are, respectively: water, 68 and 88; ash, 14 and 11; lipid, 21 and one (Fleharty et al., 1973). Adult lipid content. however, is higher in winter than summer. Western harvest mice preferably consumed fresh water during controlled experiments, but some salt water can be tolerated (Fisler, 1963). In fact, R. m. limicola consumed approximately twice as much 25% sea water than tap water in such experiments, and maintained constant body weight on 1.0 M NaCl solution (MacMillen, 1964). Western harvest mice have an exceptionally high evaporative water loss of 1.35 mg H,O/cc 0, consumed (Coulombe, 1970). and may reduce water loss in salt marshes by concentrating urine chlorides (MacMillen, 1964). R. megalotis can perceive soundwaves of 35,000 and 23.000 vibrations per second on hot-dry and cold-rainy days, respectively (Davis. 1927). Young mice squeak frequently, but adult vocaliza- tions are rare unless courting, fighting, or injured. ONTOGENY AND REPRODUCTION. Most reproduc- tive activity occurs from early spring tolate autumn, with reduced midsummer activity, but these mice do breed t ear-round in the warmer parts of their geographic range. Females become sexually mature in just over four months of age'and are polyestrous. Each of two females kept in optimal captive conditions gave birth to 14 litters in a single year (Bancroft. 1967); one produced a total of 58 young (litter size ranged from two to six) and the other 57 (litter size two to five). Males are polygamous, and dominant males copulate with females in estrus (Fisler, 1965). The male venter contacts the female lower back when copulating; there is no locking or thrust- ing. Ejaculation occurs after the first intromission and multiple ejaculations are possible (Dewsbury. 1975). Postpartum estrus is known. One to nine fetuses (Long, 1%2) have been reported; 75 . pregnant females from Nebraska had an average of 4.3 (Jones, 1%4), whereas 41 from California averaged 3.8 (Fisler, 1965). Young are born after a gestation period of 23 to 24 days. Neonates are pink, hairless (except vibrissae), and have closed eyes and ears. They weigh 1.0 to 1.5 g and are 7.0 to 8.0 mm in length at birth (Jackson, 1961). Lightly haired young begin to crawl after five days and have erupting mandibular incisors (Smith, 1936; Svihla. 1931). The eyes and ears open between day 11 and 12. and weaning is complete in 24 days. The sex ratio evidently is about even at birth, but males were found by F'isler (1971) to predominate in all age classes thereafter except among old animals, when there was a predominance of females. Western harvest mice have three characteristic pelages during their lifetime. The juvenile pelage is short. relatively sparse, and grayish brown. Postjuvenile molt "occurs at an early age, perhaps frequently before the young leave the nest" (Jones and Mursaloau. 1%1). The subadult pelage is thicker, longer, and brighter than that of juveniles but duller than the pelage ofadults. Adults molt twice annually-in spring and autumn (Jones and Mursaloau, 1961). Spring molt proceeds posteriorly on the dorsum and venter, the latter being completed first. Autumnal molt is irregular. Molt is delayed in pregnant or lactating females. In summer the dorsal pelage is short (5 to 6 mm), sparse, and brownish to dark brownish on the dorsum, sides, and flanks; the venter is grayish. The pelage of winter is long (8 to 9 mm), denser, buffy dorsally and laterally, and the venter is whitish; also, the tail is more distinctly bicolored in the winter. Senility in western harvest mice begjns to occur at about 45 weeks of age and is accompanied by reduced litter size in females (Bancroft. 1967). Jones and Mursaloau (1961) suggested that old animals may have difficulty in completing seasonal molt. Fisler (1971) found essentially a complete turnover of individuals annually in California populations. few mice reaching the age of 12 months. ECOLOGY. Western harvest mice typically inhabit grassy and weedy habitats such as overgrown pastures. meadows, fence- rows, fallow fields, and borders of agricultural and riparian areas. and not infrequently represent one of the most common mammals in such habitats. Individuals also are known from desens. salt marshes, and pine-oak forests. R. megalotis is partially sympatric with at least eight other species of harvest mice. and although "there are records of occurrence of megalotis with each of these species" (Hooper, 1952). it is separated ecologically from ravi- ventris (Fisler, 1965) and montanus (Hill and Hibbard, 1943). Mul- tiple captures with R. fulvescenr and Baiomys taylon have been reported in live traps in Durango (Peterson, 1975). Spherical nests usually are located on the ground under heavy grass, bushes, weeds. or fallen logs. and are approximately 125 mm in diameter. Some nests are built (up to 1 m) above the ground in small shrubs. The nest is composed of plant fibers with an inner layer of finer plant "down." There are one or more openings near the base. Individuals have been reported as nesting in burrows in Illinois (Birkenholz, 1967). Meserve (1977) reported circular or elliptical home ranges in California that averaged about 3.525 mS. Density estimates vary from 4.8 per acre (about 11.9 per ha) in Washington (Gray, 1943) to 4.0 per ha in New Mexico (Whitford, 1976); the New Mexico population. however, increased to 60 per ha when ground vege- tation became dense after September rains. Fisler (1966) recorded 330 feet (about 102 m) as the farthest distance between captured points of mice on a study area in California. although Brant (1%2) earlier estimated 225 feet (about 70 m) as the average maximum distance between captures for R. megalotis. "Homing" abiity was demonstrated by mice displaced by Fisler (1966) up to 1,000 feet (about 308 m) from their home areas. This species is primarily granivorous, but individuals also consume herbaceous material and lepidopteran larvae (Meserve, 1976; Whitaker and Mumford, 1972). Natural predators include owls, hawks, snakes. canids, mustelids. felids, and scorpions (Hall. 1946). Cannibalism infrequently occurs among cagemates; in fact, R. megalotis is among the most tolerant of small mammals in that individuals in captivity frequently huddle together and even do so witb mice of other species. When placed in an snificial enclosure witb Onychomys leucogaster, western harvest mice were killed within three hours (Ruffer, 1%8). No antagonistic behavior was reported when caged under conventional conditions with Mus mucculw (Catlett and Shellhammer. 1962); however, water deprivation resulted in cooperative interspecific attacks and cannibalism on female R. megalotis and then on female M. mrrsculus. R. megalotis frequently uses the runways of Microrus and Sigmodon (Hall, 1946). but does not assist in runway main- tenance (Pearson, 1959). There appears to be no tendency for western harvest mice to avoid Microtus in Californian runways (Pearson, 1960a). Numerous parasites are reported from Reithrodontomys megalotis. Endoparasites include the protozoan Trypanosoma sp. (Davis, 1952), acanthocephalan Monilgoonnis clarkii (McKeever, 1963), cestode Hymenolepis diminuta, and nematodes Syphacia obveleta and Rictulariu colorademis (Rankin, 1945). Ectopara- sites found on western harvest mice include fleas (Siphonaptera) Epitedia wenmani and Orchopeas leucopus, and chiggers (Aca- rina) Leeuwenhoekia americana. Trombicula alfreddugesi, T. li- pwskyi, T. peromysci, T. diwrsa, and T. hungerfordi (Loomis, 1956). and Trombicula autumnalis and T. loomisi (Kardos, 1954). Mites (Acarina) known to occur on Reithrodontomys megalotis include Dermacarus sp.. Androlaelaps fahrenholzi, Radfordia subuliger, Myocoptes sp., Hirstionyssw incomptus, H. occiden- talis, H. eutamiae, H. isabellinu, H. tricanthus, H. utahcmis, Macrocheles so.. Eubrachvlae~s debilis. and Mvobia muculi (Whitaker and-hiurnford, i972): Verts (1960) also;eported Hep- lopleura hesperomydis (Anopleura). BEHAVIOR. Western harvest mice are nocturnal, and - more active on moonless and rainy nights in California (Pearson, 196011). In addition, increased activity was apparent when live traps were set adjacent to rodent runways. Holes in nests are repaired immediately and, because several nests are constructed and utilized on different occasions, only old nests are fouled with excrement. "Breeding females are partic-
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ROY E. DAWSON SEASONAL PARK RANGER
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historical (Simpson 1965). The obje
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qauru Ao 1 IeA lap Inog suo K qeao
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Figure = 4 Trrnsect locations 111 1
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Table 1. Selected study habitats (A
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ats and extirpated species from the
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Table 3 Site and Transect Locations
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faunal elements are represented by
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Onvchomv. Nwthwn Grasshopper House
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8 House House Order ~arni vora Carn
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t mnis Jatrans Coyote Canis JUDW 6r
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ermwhi lus ) rtcrrl i s 601 den-man
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.Order Insectivwa panus Dwarf Shrew
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Order Insectivora WNDEROSA PINE cin
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individuals were caught in pitf a1
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REFERENCES Armstrong, Dm PI. 1972.
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Order Marsupi carnivora I POTENTIAL
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t h r m ncarl oti; Uestern Harvest
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SPECIES ACCOUNTS OF OBSERVED &NI MA
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FIGURE 2. Skull and jaw of Zapw hud
Page 42 and 43: 0 a douthitti, to be more abundant
Page 44 and 45: and 22 October, 1 November (2), and
Page 46 and 47: CryptOtis parva. By John 0. Whitder
Page 48 and 49: MAM!tIALIAN SI'ECIES NO. 43 abscnt.
Page 50 and 51: MAMMALIAN SPECIES NO. 43 and Wharto
Page 52 and 53: MAMMALIAN SPECIES NO. 43 7 Dryden,
Page 54 and 55: MAMMALIAN SPECIES No.'56. pp. 1-3.
Page 56 and 57: MAMMALIAN SPECIES NO. 56 / Known he
Page 58 and 59: 2 MAMMALIAN SPECIES 79 LUPUS pambas
Page 60 and 61: a &=station 4 MAMMALIAN SPECIES 79
Page 62 and 63: itt~riality). In Arkanras. Gipson a
Page 64 and 65: a Horn. of facial expressions in ca
Page 66 and 67: Spermophilus tridecemlineatus. By D
Page 68 and 69: MAMMALIAN SPECIES 103 3 ing emergen
Page 70 and 71: MAMMALIAN SPECIES 103 5 ground squi
Page 72 and 73: 2 FIGURE 1. Skull of Sylvilagus aud
Page 74 and 75: LITERATURE CITED Allen, J. A. 1877.
Page 76 and 77: FIGURE 2. Skull and mandible of Syl
Page 78 and 79: 4 MAMMALIAN SPECIES 136 1939). The
Page 80 and 81: - 1904. Mammals from Southern Mexic
Page 82 and 83: a Pelton, 8 MAMMALIAN SPECIES 136 -
Page 84 and 85: 2 MAMMALIAN SPECIES 159 FIGURE 1. D
Page 86 and 87: a and a dent 4 MAMMALIAN SPECIES 15
Page 88 and 89: Q f Microtus prnnsvlvanicus) as a l
Page 90 and 91: 5 8 MAMMALIAN SPECIES 159 ! eters o
Page 94 and 95: MAMMALIAN SPECIES 167 Coulombe. H.
Page 96 and 97: Odocoileus hemionus. 'B~ Allen E. A
Page 98 and 99: MAMMALIAN SPECIES 219 responsible f
Page 100 and 101: MAMMALIAN SPECIES 219 captive 0. h.
Page 102 and 103: MAMMALIAN SPECIES 219 Anderson. A.
Page 105 and 106: Neotoma mexicana. e, John E. Comely
Page 107 and 108: MAMMALIAN SPECIES 262 The baculum o
Page 109 and 110: MAMMALIAN SPECIES 262 during severa
Page 111 and 112: MAMMALIAN SPECIES 262 MURRAY. K. F.
Page 113 and 114: L 10 mrn FIG. 2. Dorsal, ventral, a
Page 115 and 116: 4 MAMMALIAN SPECIES 272 the facial
Page 117 and 118: direction of the danger stimulus; w
Page 119 and 120: 8 MAMMALIAN SPECIES 272 LAYNE. J. N
Page 121 and 122: EASTERN COTTONTAIL -Sy lvilaws f lo
Page 123 and 124: --39- DESERT COTTONTAIL Sylvilagus
Page 125 and 126: -- 48-- THIRTZEN-LINED GmUND SQUIRR
Page 127 and 128: BLACK-TAILED PRAIRIE DOG Cynomys lu
Page 129 and 130: Thomomy s talpoides Distribution.-T
Page 131 and 132: WESTERN EARVEST MOUSE 'Reithrodonto
Page 133 and 134: --69-- MEXICAN WOODRAT ~istribution
Page 135 and 136: -- 76- PRAIRIE VOLE Microtus ochrog
Page 137 and 138: COYOTE Canis latrans ~istributian--
Page 139 and 140: Odocoileus hemionus Distribution--T
Page 141 and 142: Common Name Scientific Name Habitat
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OCTOBER 1989 - City of Boulder

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